The present invention disclosed herein relates to a radio frequency receiver, and more particularly, to a radio frequency receiver for removing out-of-band interference signals or jamming signals.
To remove interference signals or jamming signals in frequency bands other than a specific band, Surface Acoustic Wave (SAW) filters are widely used in base stations or terminals in contemporary wireless communication systems.
Terminals used in next-generation mobile communication such as LTE-Advanced should be capable of multi-band radio communication. Thus, front-end architectures of radio frequency receivers in the terminals tend to be complicated and expensive. For Multi-Input Multi-Output (MIMO), in particular, the number of filters will increase in proportion to the number of antennas, and the front-ends will become more complicated in typical radio frequency receivers. Accordingly, SAW-less technologies, which can reduce the number of SAW filters or eliminate the SAW filters, are required.
Representative methods of implementing a SAW-less receiver include using a TX canceller, an on-chip filter with bonding-wire inductors, an on-chip filter with active inductors, and a passive mixer having stop-band rejection characteristics.
Using a TX canceller has limitations in that noise figure performance of a receiver is degraded, interference rejection performance changes according to group delay characteristics, and cross modulation distortion performance is degraded due to non-linearity. Using bonding-wire also has limitations in that bonding wire properties change in an actual manufacturing process, thus failing to ensure uniform quality. Using an on-chip filter with active inductors also has limitations in that noise figure is not better than passive inductors due to thermal noise generated by active devices, and active devices consume more power and their characteristics change more easily than passive inductors. The use of a stop-band rejection passive mixer is applied to a portion of Qualcomm Incorporated's commercial chips. However, in order to be applied to broadband systems such as LTE-Advanced, higher-order variable filter characteristics are required in comparison with the existing CDMA system.
For systems such as CDMA that have a relatively narrow broad bandwidth (of 1.25 MHz, for example), typical SAW-less receivers can remove jamming signals to some degree because the duplex gap between a desired signal frequency and a jamming signal frequency is sufficiently greater than a signal bandwidth by about 40 times. However, in broadband systems such as LTE, typical SAW-less receivers cannot sufficiently remove jamming signals.